Apparatus for controlling output from engine on crawler type tractor

ABSTRACT

At the time of starting movement as well as at the time when a crawler type tractor, e.g., a bulldozer for performing a dosing operation and a ripping operation is held in a three-point grounding state, an output from an engine (10) is automatically reduced further from a normal cut-off state, whereby an operator is not required to depress a deceleration pedal (13). Consequently, a burden to be borne by him can be reduced substantially.

TECHNICAL FIELD

The present invention relates generally to a crawler type tractor, e.g.,a bulldozer having a blade, a ripper or the like attached thereto toperform a bulldozing operation, a ripping operation or the like. Moreparticularly, the present invention relates to an apparatus forcontrolling an output from an engine installed on the crawler typetractor wherein the engine output is automatically controlled in anoptimum manner based on a shoe slip at the time of starting movement ofthe vehicle (crawler type track), at the time when the vehicle is heldin a neutral state or at the time when the vehicle is held in athree-point grounding state.

BACKGROUND ART

Generally, a crawler type tractor, e.g., a bulldozer or the like vehicleruns such that an output from an engine installed on the vehicle istransmitted to sprockets via a power line comprising a torque converter,a speed changing unit, bevel gears, a steering clutch, a steering brakeand a final speed reduction unit and thereby track shoes extending roundthe sprocket wheels are driven.

On the other hand, a target engine speed of the engine on the crawlertype tractor is set to a predetermined value by a throttle lever. Oncethe target engine speed is set, an output torque generated by the engineis controlled to reach the target engine speed by controlling a quantityof fuel to be injected. Usually, the crawler type tractor is equippedwith a deceleration pedal so that the engine output can be reduced to avalue corresponding to an extent of depressing of the deceleration pedalwhich has been depressed by an operator.

Tractive power generated by the engine during running of the crawlertype tractor is related to a shoe slip rate representative of shoe slipappearing between the track shoes and the ground surface. As the shoeslip increases, the tractive power increases correspondingly, until theshoe slip rate reaches a predetermined limit value. However, if the shoeslip rate exceeds the predetermined limit value, the track shoes areuselessly caused to slip with the result that an engine output from theengine on the crawler type tractor fails to be effectively utilized as atractive power. This leads to not only loss of energy but also wear ofthe track shoes within a short period of time.

Hitherto, e.g., when shoe slip occurs due to increased load during asoil heaping operation with the use of a blade or during a rippingoperation with the use of a ripper unit attached to the bulldozer, anoperator senses an occurrence of shoe slip and depresses thedeceleration pedal to reduce the engine output. At the same time, heactuates a working unit actuating lever to alleviate the engine load tolower the tractive power. In other words, a problem arising due to anoccurrence of shoe slip has been heretofore eliminated by theaforementioned complicated actuations which require a highly trainedskill.

However, since a controlling operation for adequately compensating theshoe slip by an operator's actuation has been performed by sensing ofthe shoe slip, depressing of the deceleration pedal with his foot andactuating of levers for working units with his hand, he feelscomplicated and moreover he is required to pay close attention to hisactuations. In practice, since he reduces an output from the engineafter an occurrence of shoe slip, it is unavoidable that the shoe sliplasts for a certain period of time. In addition, some operators oftencause useless slip due to careless inattention. In this case, it may beimpossible to completely prevent an occurrence of such shoe slip.Particularly, when the bulldozer collides against a hard rock-bed duringa ripping operation, the result is that the rear part of a vehicle bodyis raised up without piercing of a ripper into the rock-bed so that thebulldozer is brought in a three-point grounding state wherein thevehicle body comes in contact with the ground surface at three points,two of them being located at the fore parts of both crawler belts andthe other one being located at the foremost end of the ripper. Once thevehicle is held in the three-point grounding state, an apparent load isreduced and a vehicle speed increases in excess of a required one.Consequently, the ripper can be pierced into the rock-bed only with muchdifficulty or it cannot be pierced into the rock bed any more. In suchcase, it is impossible to release the bulldozer from the three-pointgrounding state, unless an operator depresses the deceleration pedal toreduce an output from the engine.

In addition, the vehicle has a low shoe slip rate and receives a smallmagnitude of load at the time of starting movement thereof. Thus, it isnatural that a vehicle speed increases in excess of a required one,whereby the ripper is incorrectly pierced into the rock-bed during aripping operation. Therefore, there arises a problem that a long periodof time is required until the ripper is pierced into the rock bed by apredetermined depth. To eliminate this problem, an operator is requiredto depress the deceleration pedal to reduce a vehicle speed even at thetime of starting movement of the vehicle. However, so as to allow thevehicle speed to be adequately raised up via a very low speed, a lowspeed and an intermediate speed, he should be trained to a considerablyhigh level. This is because if he is an untrained operator, he will notbe able to properly deal with the aforementioned malfunction andinconvenience.

In general, with such a crawler type tractor as described above, while atransmission is held in a neutral state, the engine is fully rotated,unless an operator depresses the deceleration pedal. For this reason, tosave fuel cost, he is required to depress the deceleration pedal atevery time when the vehicle starts its running, while the transmissionis held in the neutral state. In a case where he depresses thedeceleration pedal after starting movement of the vehicle or at the sametime as the starting movement of the vehicle, the engine speed decreasesimmediately due to an inertia of the engine, resulting in quick startingmovement of the vehicle being achieved. Thus, another problem is thatcorrect actuation of the deceleration pedal is absolutely necessary,e.g., to perform a ripping operation at a certain fixed location.

The present invention has been made with the foregoing background inmind.

An object of the present invention is to provide an apparatus forcontrolling an output from an engine installed on a crawler type tractorwherein an operator is not required to actuate a deceleration pedalduring a ripping operation and a three-point grounding state of thevehicle due to incapability of piercing of a ripper into a hardrock-bed.

Another object of the present invention is to provide an apparatus forcontrolling an output from an engine installed on a crawler type tractorwherein while a transmission is held in a neutral state, an engine speedis automatically reduced to a predetermined one to save fuel cost andprevent quick starting movement of the vehicle.

Another object of the present invention is to provide an apparatus forcontrolling an output from an engine installed on a crawler type tractorwherein the vehicle can continuously run for a certain operation at anacceptable shoe slip rate without necessity for actuating thedeceleration pedal.

DISCLOSURE OF THE INVENTION

To accomplish the above objects, there is provided according to a firstaspect of the present invention an apparatus for controlling an outputfrom an engine installed on a crawler type tractor, wherein theapparatus comprises tractive power characteristics outputting means foroutputting first tractive power characteristics having a high outputpart of the engine output cut therefrom and second tractive powercharacteristics for allowing the engine output to be reduced furtherfrom the first output characteristics by a predetermined value, startingmovement state detecting means for detecting the state of startingmovement of the crawler type tractor, means for selecting the secondtractive power characteristics and reducing the engine output, whenstarting movement of the crawler type tractor is detected by thestarting movement state detecting means, and means for gradually raisingup the engine output from the second tractive power characteristics tothe first tractive power characteristics within a preset period of timeafter the engine output is reduced.

Namely, according to the first aspect of the present invention, when thecrawler type tractor starts its running, the engine output is oncereduced and thereafter it is gradually restored to the original firsttractive power characteristics within the preset period of time.

Therefore, excessive increasing of a vehicle speed immediately afterstarting movement of the vehicle can be suppressed without necessity foractuation of the deceleration pedal with an operator s foot, whereby aripping operation as well as a bulldozing operation can be performed ata high efficiency.

According to a second aspect of the present invention, there is providedan apparatus for controlling an output from an engine installed on acrawler type tractor wherein the engine output is reduced in accordancewith preset tractive power characteristics, wherein the apparatuscomprises neutral state detecting means for detecting the neutral stateof a transmission and means for automatically reducing the preset enginespeed down to a preset engine speed, when the neutral state is detectedby the neutral state detecting means.

Namely, according to the second aspect of the present invention, whilethe transmission is held in the neutral state, fuel cost can be reducedby automatically reducing the present engine speed down to a suitableone. In addition, rapid starting movement of the vehicle can be avoidedand a ripping operation can effectively be performed at a fixedlocation.

Further, according to the third embodiment of the present invention,there is provided an apparatus for controlling an output from an engineinstalled on a crawler type vehicle, wherein the apparatus comprisestractive power characteristics outputting means for outputting firsttractive power characteristics having a high output part of the engineoutput cut therefrom and second tractive power characteristics forallowing the second output to be reduced further from the first tractivepower characteristics by a predetermined value, three-point groundingstate detecting means for detecting the state of three-point groundingof the crawler type tractor and means for selecting the second tractivepower characteristics and reducing the engine output, when the state ofthree-point grounding is detected by the three-point grounding means.

The three-point detecting means detects that the vehicle is held in thethree-point grounding state, e.g., when it detects the number of times(the number of periods) wherein an amplitude of accelerated vibration ofthe vehicle continuously exceeds a preset value and the detected numberof times exceeds a preset one.

Namely, according to the third aspect of the present invention, when itis detected that the vehicle is held in the three-point grounding state,the engine output is automatically reduced from the present level ofengine output down to a predetermined value, whereby the three-pointgrounding state is eliminated. When it is detected that the three-pointgrounding state has been eliminated, the reduced engine output isrestored to the original first tractive power characteristics.

Therefore, according to the third aspect of the present invention, thethree-point grounding state can automatically be eliminated withoutnecessity for actuating the deceleration pedal, whereby a load to beborne by an operator can be diminished.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram which schematically illustrates an apparatusfor controlling an output from an engine installed on a crawler typetractor in accordance with an embodiment of the present invention,

FIG. 2 is a schematic plan view which illustrates by way of example adriving power transmission mechanism for a bulldozer,

FIG. 3 is a fragmentary front view which shows part of an operationmonitor panel for the apparatus,

FIG. 4 is a block diagram which schematically illustrates innerstructure of a tractive power calculating section in the apparatus,

FIG. 5 is a time chart which illustrates by way of example acceleratedvibration at the time when the vehicle is held in a three-pointgrounding state,

FIG. 6 is a flowchart which illustrates operations to be performed bythe apparatus in accordance with a three-point grounding correctionmode,

FIG. 7 is a block diagram which schematically illustrates by way ofexample inner structure of an engine output controlling section in theapparatus,

FIG. 8 is a graph which illustrates by way of example basic tractivepower characteristics of the apparatus,

FIG. 9 is a graph which illustrates by way of example tractive powercharacteristics of the apparatus having slip correction added thereto,

FIG. 10 is a graph which illustrates by way of example tractive powercharacteristics of the apparatus at the time of starting movement of thevehicle,

FIG. 11 is a graph which illustrates by way of example tractive powercharacteristics of the apparatus at the time of three-point grounding,

FIG. 12 is a graph which schematically illustrates a relationshipbetween a vehicle speed and a tractive power derived from engine/torqueconverter matching characteristics of the apparatus,

FIG. 13 is a graph which schematically illustrates an engine speed atthe time when the vehicle is held in a neutral state,

FIG. 14 is a flowchart which schematically illustrates all operations tobe performed by the apparatus in accordance with the embodiment of thepresent invention, and

FIG. 15 is a flowchart which schematically illustrates operations to beperformed by the apparatus at the time of starting movement of thevehicle.

BEST MODE FOR CARRYING OUT THE INVENTION

Now, the present invention will be described in detail hereinafter withreference to the accompanying drawings which illustrate an apparatus forcontrolling an output from an engine installed on a crawler typetractor. It should be noted that this embodiment is described on theassumption of a case where a bulldozer performs a ripping operation anda dosing operation.

As shown in FIG. 1, the bulldozer is equipped with an opposing pair ofcrawler belts 2 on both sides of a vehicle body 1. Further, thebulldozer includes a blade 3 in front of the vehicle body 1, and theblade 3 rises and lowers in response to extension or contraction of ablade cylinder 4. In addition, the bulldozer includes a ripper shank 5behind the vehicle body 1, and the ripper shank 5 rises and lowers inresponse to extension and contraction of a lift cylinder 6 and tilts inresponse to actuation of a tilt cylinder 7.

A throttle lever 9 is provided in the form of an actuation lever forsetting a target engine speed for an engine 10. Once the target enginespeed is set by the throttle lever 9, a central processing unit(hereinafter referred to as a CPU) 90 controls the engine 10 via agovernor 11 and a fuel injection unit 12 such that the engine 10generates a torque corresponding to the thus set target engine speed.

A deceleration pedal 13 is provided in the form of a foot pedal which isdepressed by an operator to reduce the torque generated by the engine10. When the pedal 13 is depressed by an operator's foot, a strokequantity detecting sensor attached to the pedal 13 detects a quantity ofstroke so that the torque generated by the engine 10 is reduced inproportion to the quantity of stroke.

A blade lever 15 is provided in the form of a manual actuating leverwhich carries out rising, lowering, angling and tilting of the blade 3.The blade cylinder 4 and a frame 16 are extended or contracted inresponse to actuation of the blade lever 15.

The levers 14 and 15 are provided with a working unit lever detectingsensor 17 for detecting the present position to which they are actuated,respectively.

FIG. 2 is a schematic plan view of a power transmission mechanism forthe bulldozer in FIG. 1 as seen from the above.

As is apparent from FIG. 2, an output from the engine 10 is transmittedto a driving shaft 20 via a torque converter 18 and a speed changingunit 19. Driving power derived from the driving shaft 20 is thentransmitted to an opposing pair of steering clutch brakes 21, anopposing pair of final speed changing units 22 and an opposing pair ofsprockets 23 each pair of which are arranged on opposite sides of thedriving shaft 20. Each of the sprockets 23 meshes with the crawler belt2. With such construction, the crawler belts 2 are driven with tractiveforce which varies with a total speed reduction ratio which isdetermined by components arranged within the range from input/outputshafts of the speed changing unit 19 till the sprockets 23.

An output shaft of the engine 10 is provided with an engine speed sensor24 for detecting the present engine speed and an output shaft of thetorque converter 18 is provided with a torque converter output shaftrotation speed sensor 25 for detecting the present torque converterspeed. In addition, the speed changing unit 19 is provided with a speedstage detecting sensor 26 (in the form of a clutch hydraulic pressuresensor) for detecting the presently selected speed stage.

Further, as shown in FIG. 1, the bulldozer is equipped with anacceleration sensor 27 for detecting acceleration in the longitudinaldirection of the vehicle body 1. An operation monitor panel 28 is placedin front of an operator's seat so as to allow an operator to selectoperative conditions required for the bulldozer and display thereonmonitor informations necessary for him. The operation monitor panel 28includes an operation mode selection panel as shown in FIG. 3. Theoperation mode selection panel is provided with a rock-bed modeselection switch 29 for a dozing operation so as to allow him to selecta soft rock-bed or a hard rock-bed when the switch 29 is shifted to ON.If he selects a hard mode, an LED 29a corresponding to the hard mode isilluminated, and if he selects a soft mode, another LED 29bcorresponding to the soft mode is illuminated. The CPU 90 carries outoptimum engine torque control corresponding to the selected mode.

The operation monitor panel 28 includes a slip control switch 30 androck-bed selection switches 31 and 32 for a ripping operation. The slipcontrol switch 30 is provided in the form of a switch which selectivelydetermines whether an engine torque control (slip control) should becarried out or not so as to prevent an excessive quantity of slippagefrom taking place. When the slip control switch 30 is depressed, the LED30a is illuminated. The slip control mode selection switches 31 and 32are provided in the form of a soil nature mode switch, respectively,which allows an operator to arbitrarily select one of soil nature modes1 to 5 corresponding to operative conditions (environmental conditions)of the bulldozer, i.e., the present nature of soil. When one of the slipcontrol mode selection switches 31 and 32 is selectively depressed, oneLED corresponding to the selected soil nature mode is illuminated.

A plurality of outputs from the engine speed sensor 24, the torqueconverter output rotation sensor 25, the speed stage detecting sensor26, the working unit lever detecting sensor 17, the acceleration sensor27 and the operation monitor panel are inputted into the CPU 90.

The CPU 90 includes an operative condition setting section 40 whichselects one of the hard or soft mode for a dozing operation, the soilnature modes 1 to 5 for a ripping operation and a mode having no shoeslip control carried out for the apparatus, based on input conditionsfor the operation monitor panel 28 shown in FIG. 3. The selected modesignal M is inputted into an engine output controlling section 50.

The CPU 90 derives a tractive power F in a tractive force calculatingsection 41 based on the detected engine speed Ne and torque converteroutput shaft rotation speed N_(T). Specifically, as shown in FIG. 4,first, the CPU 90 calculates an e value in accordance with the followingequation, based on the torque converter output shaft rotation speedN_(T) detected by the torque converter output shaft rotation speedsensor 25 and the engine speed Ne detected by the engine speed sensor 24

    e=N.sub.T /Ne                                              (1)

Next, the CPU 90 derives a primary coefficient t_(p) from the graphicrelationship shown in FIG. 4, based on the e value which has beenderived in accordance with the equation (1).

Next, the CPU 90 derives a torque converter input shaft absorptiontorque t_(e) in accordance with the following equation (2), based on thethus derived primary torque t_(p) and the engine speed N_(e) detected bythe engine speed sensor 24.

    t.sub.e =t.sub.p ×(Ne/1000).sup.2                    (3)

In addition, the CPU 90 derives a torque ratio t from the graphicrelationship shown in FIG. 4, based on the e value which has beenderived from the equation (1). The CPU 90 calculates the tractive powerF in the following manner, based on the thus derived ratio t, the torqueconverter input shaft absorption torque t_(e) derived in accordance withthe equation (2) and a predetermined coefficient K_(x).

    F=Kx·t·t.sub.e                           (3)

Incidentally, the present invention may be carried out for deriving thetractive force F based on a torque inputted into the speed changing unit19, a total speed reduction ratio derived within the range from an inputshaft of the speed changing unit 19 to the sprocket 23 and a powertransmission efficiency. Alternatively, the present invention may becarried out for directly detecting the tractive force F using a torquesensor or the like means.

Next, the CPU 90 calculates an ideal vehicle speed v_(T) for the crawlerbelts 2 in an ideal vehicle speed calculating section 42, based on thetorque converter output shaft rotation speed N_(T), the speed stagesignal TM detected by the speed stage detecting sensor 26 and the totalspeed reduction ratio derived within the range from the speed changingunit 19 to the sprockets 23. Here, the ideal vehicle speed v_(T)designates a vehicle speed without any occurrence of slippagerepresented by zero slip, i.e., a crawler belt speed. It should be addedthat the present invention may be carried out for deriving the idealvehicle speed v_(T) by directly detecting the number of rotations of thesprockets 23.

Next, the CPU 90 derives an actual vehicle speed v in an actual vehiclespeed calculating section 43 by integrating the acceleration α which hasbeen derived by the longitudinal acceleration sensor 27. It should benoted that since the acceleration of the vehicle body 1 is a compositeacceleration consisting of an acceleration represented by α=dσ/dt basedon the actual vehicle speed v, an acceleration attributable toinclination of the vehicle body (ground surface) and an accelerationattributable to vibration of the vehicle body, the CPU 90 performs acorrective calculation for deriving the acceleration α based only on theactual vehicle speed v by practically subtracting the accelerationattributable to inclination of the vehicle body and vibration of thevehicle body from the actually detected acceleration. Further, it shouldbe noted that the vehicle speed v may not be detected by integrating theacceleration but may directly be detected using predetermined sensors,e.g., a Doppler sensor or the like means.

Next, the CPU 90 calculates a slip rate SP in a slip rate calculatingsection 48 in accordance with the following equation, based on theactual vehicle speed v calculated in the actual vehicle speedcalculating section 43 and the ideal vehicle speed v_(T) calculated inthe ideal vehicle speed calculating section 42.

    S P=1-ν/ν.sub.T

The CPU 90 detects a state of starting movement of the vehicle in astarting movement detecting section 44 based on an output from theacceleration sensor 27. Specifically, the CPU 90 determines that thevehicle starts its movement when the acceleration α exceeds a presetvalue and then inputs the resultant starting movement detection signalST into the engine output controlling section 50.

Next, the CPU 90 detects in a neutral detecting section 45 that thetransmission is held in a neutral state in response to the speed stagesignal TM and then outputs the resultant detection signal N to theengine output controlling section 50.

Further, the CPU 90 detects in a three-point grounding detecting section46 based on the output α from the acceleration sensor 27 that thevehicle is brought in a three-point grounding state wherein the vehiclebody 1 comes in contact with the ground at three points, i.e., theripper and the both caterpillars and then outputs the resultantdetection signal TS to the engine output controlling section 50.

Specifically, as shown in FIG. 5, when the vehicle body 1 is brought inthe three-point grounding state, it vibrates with the longitudinalacceleration α and a series of amplitudes H₁, H₂, --- H_(n) of thevibration rapidly increase compared with a case where it is not held inthe three-point grounding state, while continuously maintaining theincreasing state. To this end, the CPU 90 detects in the three-pointgrounding state detecting section 46 that the vehicle body 1 has beenbrought in the three-point grounding state, when it has been found thatthe vibration having an amplitude larger than a predetermined amplitudeH_(k) sequentially occurs by a predetermined number of times n_(c) (apredetermined number of periods represented by, e.g., n_(c) =8).

FIG. 6 is a flowchart which schematically illustrates detectingoperations to be performed by the CPU 90. The CPU 90 derives in thethree-point grounding detection section 46 an amplitude of accelerationfrom the detected acceleration at all times (step 100) and then comparesthe thus derived acceleration with a predetermined amplitude H ofacceleration (step 101). When the CPU 90 has detected from the abovecomparison that the amplitude of vibration is larger than a presetvalue, it examines by how many times of periods the above detection issequentially carried out (step 102). When it has been found thatdetection is sequentially carried out in excess of the preset timesn_(c) of periods while an amplitude of the vibration exceeds a presetvalue, the CPU 90 determines that the vehicle body 1 has been brought inthe three-point grounding state. When the CPU 90 detects in thethree-point grounding detection section 46 that the vehicle body 1 isheld in the three-point grounding state, it outputs the detection signalTS to the engine output controlling section 50. It should be added thata series of processings later than the steps 103 in FIG. 6 will bedescribed later.

Next, the CPU 90 determines an operative state of the respective workingunits, i.e., the ripper 5 and the blade 3 in a working unitraising/lowering detecting section 47 based on an output from the leveractuation detecting sensor 17 which detects the present operative stateof the ripper lever 14 and the blade lever 15 and then outputs theresultant determination result G_(a) to the engine output controllingsection 50.

The engine output controlling section 50 is intended to perform acontrolling operation for increasing or decreasing an output from theengine. Inner structure of the engine output controlling section 50 isschematically illustrated in FIG. 7. In this connection, it should benoted that only structure for performing a ripping operation isillustrated in FIG. 7. Further, it should be noted that the engineoutput controlling section 50 carries out an engine output cut-offcontrol to be described later during the ripping operation which will beperformed only at a first speed for forward movement of the bulldozer.

The engine output controlling section 50 includes a basic tractive powermode shifting portion 51 in which five basic tractive powercharacteristics with a high output part (represented by a dotted line inthe drawing) in the full performance curve of the engine 10 cuttherefrom as shown in FIG. 8 are stored corresponding to a ripping mode.The CPU 90 selects and reads one of the stored five basic tractive powercharacteristics in response to a mode signal M transmitted from anoperative condition setting section 40 and then outputs a tractive powerF_(o) (F_(o1) to F_(o5)) on five bent points of the thus read basictractive power characteristic to subsequent functional parts to bedescribed later. Here, the tractive power F_(o) on the bent points ishereinafter referred to as a basic tractive power. It should be addedthat a vehicle speed V_(o) corresponding to the basic tractive powerF_(o) is set to 0.7 km/hr in the shown case.

Referring to FIG. 7, the CPU 90 determines in a shoe slip limitdetecting section 56 whether a shoe slip rate SP transmitted from theshoe slip limit detecting section 56 exceeds a predetermined limit valueor not and then outputs a detection signal SSF when it has been foundthat it exceeds it. In the shown case, the limit value is set to 30%.

The CPU 90 executes a processing of latching a tractive power F_(a) atthe time when the detection signal SSF is inputted into a shoe sliplimit power storing portion 57. The latched tractive power F_(a) isinputted into a slip correcting portion 58 in which the latched tractivepower F_(a) is multiplied with a predetermined correcting coefficient K₁(where K₁ is smaller than 1) (see FIG. 9). This correcting coefficientK₁ is set to, e.g., 0.5 to 0.8. An output F_(c) (=K₁ ·F_(a)) from theslip correcting portion 58 is inputted into a working unit actuationcorrecting portion 59 in which the output F_(c) is adequately correctedin correspondence to actuation of the ripper lever 14. If the bulldozerperforms a ripping operation with the tractive force F_(c) which hasbeen corrected depending on a quantity of slippage, there is a dangerthat an output from the engine 10 becomes short in power or a workingspeed becomes slow. For this reason, when the ripper lever 14 isactuated, the corrected tractive power F_(c) is multiplied with aworking unit actuation correcting coefficient K_(L) (which is largerthan 1) to increase an output from the engine 10 (see FIG. 9). Thiscorrecting coefficient K_(L) varies depending on the kind of operation,e.g., lowering of the ripper, tilt-back of the ripper, raising of theripper, tilt of the ripper or the like. On the other hand, the basictractive power F_(o) which has been selected in that way is inputtedinto a starting movement correcting portion 53 and a three-pointgrounding correcting portion 54.

The engine output controlling section 50 calculates in the startingmovement correcting portion 53 a tractive power F_(s) which is correctedat the time of starting movement of the bulldozer with a reduced outputfrom the engine 10, by multiplying the inputted basic tractive powerF_(o) with a predetermined correcting coefficient K₂ (which is smallerthan 1), as shown in FIG. 10. The reduced magnitude of tractive powerF_(s) is gradually increased by a timer circuit 70 (see FIG. 1) so thatit is restored to the initial basic tractive power characteristics aftera predetermined period of time (e.g., 3 seconds) elapses.

Further, the engine output controlling section 50 calculates in thethree-point grounding correcting portion 54 a tractive power F_(D) whichis corrected at the time of three-point grounding with a reduced outputfrom the engine 10, by multiplying the inputted tractive force F_(o)with a predetermined correcting coefficient K₃ (which is smaller than1), as shown in FIG. 11.

Next, the engine output controlling section 50 selects in a shiftingcircuit 55 one of the four tractive forces F_(e), F_(o), F_(s) and F_(D)depending on the signals SSF, ST and TS and the selected tractive forceis then inputted into a target tractive power calculating portion 60. Ifthe shoe slip rate exceeds the limit value (30%) (with the signal SSFset to 1), the tractive power F_(e) is selected. If the shoe slip ratedoes not exceed the limit value (with the signal SSF set to 0), thetractive power F_(o) is selected. In addition, at the time of startingmovement of the bulldozer (with the signal ST set to 1), the tractiveforce F_(s) is selected. Further, at the time of three-point grounding(with the signal TS set to 1), the tractive power F_(D) is selected.

Tilt of the respective tractive power characteristics is preset in atarget tractive force calculating portion 60 so that the target tractivepower calculating portion 60 generates tractive power characteristicswhich are corrected by using the preset tilt of the tractive powercharacteristics with the tractive power F_(c), F_(o), F_(s) or F_(D)inputted from the shifting circuit 55 as bent points of the tractivepower characteristics and moreover the target tractive power calculatingportion 60 derives a target tractive power F_(r) corresponding to thepresent ideal vehicle speed v_(T), based on the corrected tractive powercharacteristics.

This tractive power F_(r) is inputted into a throttle command generatingportion 61 to derive from the inputted tractive power F_(r) a throttlecommand ω SET corresponding to the present crawler belt speed v_(T),i.e., a target engine speed of the engine 10.

The throttle command ω_(SET) which has been derived in that way isinputted into a minimum value selecting section 71 shown in FIG. 1. Inaddition to the throttle command ω_(SET), an output from the throttlelever 9 and an output from the deceleration pedal 13 are inputted intothe minimum value selecting section 71 so that the minimum valueselecting section 71 selects a smaller command value of the foregoingoutputs. For example, if an output generated by actuating the throttlelever 9 by an operator or actuating the deceleration pedal 13 by hisfoot is smaller than the throttle command ω_(SET), the minimum valueselecting section 71 selects a command value given by the operator whoactuates the throttle lever 9 or the deceleration pedal 13.Consequently, the apparatus of the present invention assures a highsafety of operation and a quick responsiveness to operation of theapparatus in case of an occurrence of emergency.

A quantity of fuel to be injected by the fuel injecting unit iscontrolled by inputting an output from the minimum value selectingsection 71 into the governor 11, whereby an output from the engine 10 iscontrolled adequately. FIG. 12 is a graph which schematicallyillustrates a relationship between a vehicle speed and a tractive powerwhich will be derived from an engine/torque converter matchingperformance. This relationship is established by deriving from a vehiclespeed-tractive power curve a vehicle speed which will become a targetrelative to a tractive power generated as a load and then setting atarget engine speed which will become an engine output in such a manneras to extend through an intersection as defined by the vehicle speed andthe tractive power. Then, a quantity of fuel to be injected iscontrolled via the governor 11 and the fuel injection pump 12 tomaintain the thus set engine speed.

In this case, when a detection signal N from the neutral detectingsection 45 is inputted into the engine output controlling section 50,the engine output controlling section 50 outputs a command WN_(u)corresponding to a suitable engine speed RN_(u) between an engine speedRH_(i) instructed by a high idle engine speed command WH_(i) and anengine speed RL_(i) instructed by a low idle engine speed command WL_(i)to automatically reduce the engine speed during running of the vehicleat a neutral speed down to the suitable engine speed RN_(u), as shown inFIG. 13. It should be added that the engine speed RN_(u) can arbitrarilybe varied as required.

Next, operations to be performed by the apparatus of the presentinvention as constructed in the above-described manner will be describedbelow with reference to flowcharts shown in FIGS. 14 and 15. Here, itshould be noted that description will be made as to a case where thebulldozer performs a ripping operation.

When the apparatus carries out shoe slip control, i.e, the apparatusperforms an operation relevant to structural components 56, 57, 58 and59 shown in FIG. 7, an operator shifts switches 30 to 32 on theoperation monitor panel 28 in FIG. 3 to ON to instruct shoe slip controland suitably select one of soil nature modes 1 to 5. In addition, heperforms an initial setting operation for a variety of parameters whichare required for carrying out shoe slip control (step 200 in FIG. 14).Then, he sets to a suitable value the engine speed RN_(u) at the timewhen the transmission is held in a neutral state (step 210).

When the vehicle starts its running, the engine output controllingsection 50 in the CPU 90 performs a searching operation based on theoutput N from a neutral detecting section 45 as to whether thetransmission is held in the neutral state or not (step 220). If theengine output controlling section 50 detects that the transmission isheld in the neutral state, it executes a process of reducing the presentengine speed down to the engine speed RN_(u) corresponding to thethrottle command WN_(u) by outputting therefrom the throttle commandWN_(u) which has been set at the step 210 (step 230). Consequently, theengine speed is automatically reduced to a suitable engine speed at thetime when the transmission is held in the neutral state, resulting infuel saving being achieved. Thereafter, even when the vehicle starts itsrunning at a first forward speed, it can adequately perform a rippingoperation at a predetermined position without rapid starting movementthereof.

When it has been found that the transmission is held in an operativestate other than the neutral state, the engine output controllingsection 50 performs a searching operation, based on the output ST from astart detecting section 44, as to whether the vehicle has started itsrunning or not (step 240). If it detects that the vehicle has startedits running, it executes a starting movement correction mode shown inFIG. 15.

Namely, when the engine output controlling section 50 detects that thevehicle has started its running (step 300 in FIG. 15), a startingmovement correction portion 53 in the engine output controlling section50 once reduces an output from the engine 10 (step 310). Thereafter, theengine output controlling section 50 gradually raises the reduced engineoutput up to the original basic tractive power characteristics within apredetermined period of time by using the output from a timer 70 (step320). Specifically, the engine output controlling section 50 executes apower down/up control by outputting a corrected tractive power F_(s)therefrom in accordance with the following equation on the assumptionthat K₂ designates a correction coefficient, T_(c) designates arestoration setting time and T designates a period of time that elapses.

    Fs=Of ((1-k2)T/Tc+K2)

According to the above-described embodiment of the present invention,when the bulldozer performs a lowering operation for lowering the ripperwhile the CPU 90 is carrying out starting movement control, the CPU 90cancels shortage in engine power by multiplying the output F_(s) with acorrection coefficient K_(r) (which is larger than 1) (steps 330 and340). Thereafter, the CPU 90 shifts to a normal basic tractive powermode with which the CPU 90 is to carry out control.

Then, a tractive power F_(o) corresponding to the soil mode selected bythe shifting circuit 55 in FIG. 7 is inputted into the CPU 90 while thebasic tractive power mode is maintained so that the engine output iscontrolled with any one of the five tractive power characteristics shownin FIG. 8. While the basic tractive power mode is maintained, the CPU 90executes examination as to whether or not the shoe slip rate exceeds alimit shoe slip rate (e.g., 30 %) in response to the output SSF from ashoe slip limit detecting portion 56 (step 270). When it has been foundthat it exceeds the limit shoe slip rate, the CPU 90 shifts to a slipcorrection mode as shown in FIG. 9 (step 280).

While the slip correction mode is maintained, the CPU 90 reduces anoutput from the engine 10 further so that the tractive power F_(a) atthe time when the shoe slip rate exceeds the limit value as describedabove is reduced further to the tractive power F_(c).

The shoe slip correction mode is gradually restored to the originalbasic tractive power mode, if conditions, e.g., a condition wherein theshoe slip rate is less than 20%, a condition wherein the vehicle speedexceeds a predetermined value, a condition wherein the tractive powerbecomes smaller than a predetermined value and so forth are established(step 290).

It should be noted that the basic tractive power characteristics shownin FIG. 8 are set as curves which enable the vehicle to move forwardlyat a highest speed with a maximum effective tractive power. However,when the CPU 90 determines that the bulldozer is practically held in aslippage state, it can be concluded that the tractive power F_(a)derived at that time represents a maximum effective tractive power. Inview of the aforementioned fact, the CPU 90 reduces the vehicle speed byperforming a correcting operation to reduce the basic tractive powerF_(o) down to K₂. F_(a), whereby an occurrence of slippage isdiminished. As a result, the bulldozer moves at a reduced speed whilegenerating a maximum effective tractive power which is most suitable fora working site where slippage practically occurs and moreover mostsuitable for the current ripping operation, whereby an occurrence ofslippage can be minimized.

When slippage in excess of the limit value does not occur, the CPU 90cuts off a high output part in the engine output and operates thebulldozer with basic tractive power characteristics corresponding to thepresent soil nature. Thus, the bulldozer can exhibit a maximum effectivetractive power most suitable for the working site where no slippageoccurs. If the CPU 90 increases or decreases the engine output dependingon the operative state of the ripper at the time when the basic tractivepower mode is maintained, the bulldozer can generate a maximum effectivetractive power most suitable for the present operative state of theripper at the time when the basic tractive power mode is maintained.

Further, if the CPU 90 gradually shifts the engine output from the basictractive power mode to the slip correction mode and vice versa within apredetermined period of time, e.g., 0 to 3 seconds after theaforementioned restoration conditions have been established, thebulldozer can operate smoothly without any occurrence of shock.

The three-point grounding detecting section 46 detects during theabove-described engine control, based on the vibratory state of theacceleration of the vehicle, whether the three-point grounding state isreached or not (steps 100 to 102 in FIG. 6). When a detection signal TSis inputted into the engine output control section 50 from thethree-point grounding detecting section 46, the engine output controlsection 50 executes a three-point grounding correction mode as shown inFIG. 11. Specifically, the CPU 90 calculates the corrected tractivepower F_(D) at the time of three-point grounding in a three-pointgrounding correcting portion 53 by multiplying the tractive power F_(o)having the presently selected basic tractive power characteristics witha predetermined correction coefficient K₃ and moreover the CPU 90controls the engine output so as to allow the vehicle to move with thetractive power characteristics including the tractive power F_(D) as abent point (step 103).

In this manner, at the time of three-point grounding, the engine outputis automatically reduced to an adequate engine output which assures thatthe three-point grounding state can be avoided.

Such engine output correction derived from the three-point groundingstate is canceled when the following conditions are established.Thereafter, a controlling operation is gradually restored to theoriginal basic tractive power mode (steps 104 and 105).

Conditions:

The slip rate is smaller than a set value.

The tractive force is smaller than a set value.

The vehicle speed is larger than a set value.

In this manner, while the three-point grounding state is maintained, theengine output is automatically reduced and thereby an operator is notrequired to depress the deceleration pedal.

It should be noted that the CPU 90 executes engine control based on thebasic tractive power characteristics shown in FIG. 8 as well as enginecontrol based on the slip correction shown in FIG. 9, when a shoe slipcontrol switch 30 in FIG. 3 is shifted to ON. However, if the shoeswitch control switch 30 is not shifted to ON, the CPU 90 does notperform the aforementioned controlling operation but it executes controlin accordance with the full performance curve in the same manner as innormal cases.

In a case where the bulldozer is instructed to perform a bulldozingoperation, the CPU 90 selects from a memory in the engine outputcontrolling section 50 characteristics similar to those in FIG. 8including a series of bent points, reads them and then executes controlsimilar to the aforementioned ones.

According to the above-described embodiment of the present invention,the correction coefficient K₁ at the time of an occurrence of shoe slipis set common to each nature of soil, as shown in FIG. 9. However, thepresent invention should not be limited only to this. Alternatively, adifferent correction coefficient K₁ may be set depending on one of thesoil natures 1 to 5.

Further, according to the above-described embodiment of the presentinvention, a signal representative of the present vehicle speed stage isdetected by a clutch hydraulic pressure sensor in the transmission.Alternatively, the vehicle speed stage may be detected by detecting theposition which has been assumed by the shift lever. In addition, thetractive power, the ideal vehicle speed, the actual vehicle speed, thestate of starting movement of the vehicle, the state of three-pointgrounding and so forth may be detected by employing an arbitrarydetecting method other than the method which has been employed forcarrying out the embodiment of the present invention.

Additionally, according to the above-described embodiment of the presentinvention, when the three-point grounding state is detected, the CPU 90reduces the engine output by multiplying the tractive power F_(o)derived from the basic tractive power characteristics with a correctioncoefficient K₃. Alternatively, the CPU 90 may reduce the engine outputby multiplying the tractive power at the bent point on the curverepresentative of the slip correction mode with a predeterminedcorrection coefficient, when the vehicle operates in accordance with theslip correction mode at the time of detection of the three-pointgrounding state.

Moreover, with respect to power-down control to be carried out at thetime of starting movement of the vehicle, the CPU 90 may take a logicsum consisting of detection output in the state of starting movement ofthe vehicle and detection output at the time of lowering of the ripperto carry out power-down control based on the output derived from thelogic sum. In this case, the apparatus of the present invention preventsa vehicle speed from being excessively increased during a rippingoperation which is performed at the same time when the vehicle startsits movement. Consequently, the ripping operation can be accomplishedwith good results.

INDUSTRIAL APPLICABILITY

The present invention is advantageously applicable for the purpose ofcontrolling, an engine during a ripping operation, a bulldozingoperation or the like operation with the use of a crawler type tractor,e.g., bulldozer or the like vehicle.

We claim:
 1. An apparatus for controlling output from an engine installed on a crawler type vehicle provided with a ripper shank, wherein said vehicle runs by means of left and right crawler belts to which output of the engine is transmitted via a torque converter, a transmission, a driving shaft, comprising:tractive power characteristic outputting means for outputting a basic tractive power characteristic having a characteristic of decreasing a tractive power of the vehicle as an ideal vehicle speed increases with a first gradient within a range where the ideal vehicle speed is lower than a predetermined speed and a characteristic of decreasing the tractive power as the ideal vehicle speed increases with a second gradient smaller than the first gradient within a range where the ideal vehicle speed is larger than the predetermined speed and for outputting a starting tractive power characteristic in which the output of the engine is lowered by a predetermined value from the output of the engine in the basic tractive power characteristic; starting movement detecting means for detecting starting movement of the vehicle; means for selecting the starting tractive power characteristic and reducing the output of the engine when starting movement of the vehicle is detected by the starting movement detecting means; means for gradually raising the output of the engine from the starting tractive power characteristic to the basic tractive power characteristic within a preset period of time after the output of the engine is reduced; ripper operation detecting means for detecting the lowering operation of the ripper shank; and means for raising the output of the engine by outputting a modified tractive power characteristic in which the starting tractive power characteristic is raised by a preset value when the lowering operation of the ripper shank is detected by the ripper operation detecting means.
 2. The apparatus of claim 1, further comprising:shoe slip detecting means for detecting when a shoe slip rate exceed a predetermined limit slip rate; and means for receiving a tractive power value at the time when the shoe slip detecting means detects that the limit slip rate is exceeded and for outputting a shoe slip modifying tractive power characteristic for modifying shoe slip so as to cut off the output of the engine.
 3. The apparatus of claim 1, wherein the tractive power characteristic outputting means is provided with a plurality of different basic tractive power characteristics for a ripping operating corresponding to hardness of soils to which the ripping operation is performed, and the apparatus further comprises means for selectively designating one of the plurality of basic tractive power characteristics. 